I'm a former LRS guy 504th BFSB the differences come in equipment and size of force.
I have no choice but to separate into vehicle types because that's what is the primary factor (Stryker's, Abrams (19K), Bradley's, 1068s, MATV/MRAPS)
This first part is going to be in reference to Unified Land Operations:
the difference between a Scout and Mech INF is what we do once contact is created. Rather on feet or in a fighting vehicle a scouts main purpose is to be the eyes of the commander and provide timely and accurate intelligence so that commanders can make timely decisions.
The Infantry generally is the organic unit that seeks to engage and destroy the enemy or maintain contact until the enemy force is attrited
The basic/core competencies of the jobs do not change based on mobility.
When I was a member of the 504th BFSB we had all kind of force enablers national based that would support us in our ability to be the eyes of the battlefield. You set your scouts in Observation Points along screen lines. You set your infantry in fighting positions. When I was in 1st CAV same type of enablers except lesser level more organic or division based.
Ok so that's the old BS:
What is now starting to occur is each heavy Cav Squadron now has a tank company and each troop has a FIST which provides even more lethality forward of the Infantry and a means to hold contact with the enemy. With BFVs and Abrams along the screen lines moving out of Observation Points the enemy should be generally atritted (destroyed/disrupted/degraded) more before they meet the primary fighting force.
The Infantry along with Armor, Artillery, and Engineer assets at that point along with their FIST element and tank elements should be able to attrit the remainder of the enemy force.
In all reality when you are sitting on staff planning operations the MOS seems to kind of fly out. I want my scouts with FIST and enablers (JTACs) ahead of the main fighting forces. I want my Infantry tucked away with Tankers, Artillery, and Engineers (JTACS) and I want my BDE, Support BN, and Engineers tucked away. AKA everyone supports the Infantry but everyone at any given time can be in contact but no one is expected to maintain and commit to holding the contact compared to the Infantry.
Our light scouts got fukked royally lol. I was a medic in an Artillery battalion that was used as a maneuver battalion with 2 extra infantry company attachments to help us hold our battle space. We held Khost, east of the K-G pass. Our Cav squadron had to hold everything west as a maneuver “battalion” with no additional attachments aside from some artillery dudes from the 82nd Airborne/319th FAR, that shot for both of us lol. If you’ve ever seen the documentary “hornets nest” the soldiers in ACU’s under Col. Lutzky, we’re our cav squadron. What they had to do was completely against their function lol. They came back mad AF! Not only did they have to deal with their own constant fights, their squadron CO would drag some of them over to our side to fight some more lmao.